Field of the Invention
Exemplary embodiments of the present invention relate to a method of controlling valve timing and valve duration using a continuously variable valve timing (CVVT) apparatus and a continuously variable valve duration (CVVD) apparatus; and, particularly, to a method of controlling valve timing and valve duration using a CVVT apparatus, which adjusts a valve opening time of a vehicle engine, and a CVVD apparatus which adjusts duration of a valve lift.
Description of Related Art
An internal combustion engine generates power by burning fuel and air that are supplied into a combustion chamber. An intake valve is operated by driving a camshaft for suction of air, and fuel and air are introduced into the combustion chamber while the intake valve is open. An exhaust valve is operated by driving the camshaft, and air is discharged from the combustion chamber after combustion while the exhaust valve is open.
In general, a valve switching timing is fixed such that the engine is able to obtain maximum power in a specific revolution per minute (rpm) range. Accordingly, the valve switching timing must be retarded in a low rpm range for expansion and explosion of a mixture, whereas it must be advanced in a high rpm range for discharge of the mixture after the explosion. However, if the valve timing is adjusted to be retarded, the discharge of the mixture is delayed when the engine rotates at a high speed, and if the valve is adjusted to be advanced, the compression of the mixture is delayed when the engine rotates at a low speed. As a result, the efficiency of the engine is too low.
To resolve such a problem, there has been proposed a continuously variable valve timing (CVVT) technology that changes a valve switching timing to be suitable for an engine rpm in a state in which a valve duration is fixed in order to obtain high fuel efficiency and power at both high and low speeds. Although the CVVT technology may effectively control a valve opening time, it may not change a valve duration.
To change the valve duration, there has been developed a continuously variable valve lift (CVVL) system that allows valves to be operated by different lifts according to the engine rpm. However, since a valve duration is varied but a valve lift is simultaneously changed in the CVVL system, the CVVL system has a low degree of freedom in regard of control.
To resolve such a problem, there has been developed a continuously variable valve duration (CVVD) apparatus as disclosed in Patent Document 1. The CVVD apparatus may effectively vary a valve timing and a valve duration without changing a valve lift by interlocking with a CVVT apparatus. In addition, the CVVD apparatus may set an optimum valve switching timing by independently controlling valve opening and closing times.
However, when the valve timing and the valve duration are adjusted using the CVVD and the CVVT, a desired valve timing may not be obtained due to a change in valve timing when the valve duration is varied. However, the method of controlling valve timing and valve duration using CVVD and CVVT has not been sufficiently studied to the present time.